1. Field of the Invention
This invention relates to a seat occupation judging apparatus for a vehicle.
2. Description of the Prior Art
Crew detection sensors for detecting a crew are known. The crew detection sensor is used for determining to operate a crew protection device such as an airbag or a seatbelt pre-tensioner for protecting a passenger on the assistant driver""s seat on crash.
As crew detection sensors, load sensors including a strain gage attached to a seat frame have been proposed. Crews are classified on the basis of difference in weight of crews represented by an output signal of the sensors.
Japanese patent application provisional publication No. 2000-301980 discloses such a judging technique with a sensor for detecting load distribution at a seat. Crews are judged to be either of an adult or a child on the basis of the detected load distribution at the seat.
Japanese patent application provisional publication Nos. 10-319133 and 11-11256 disclose techniques for judging the presence of a crew on a seat on the basis of variation in capacitance utilizing the effect that the passenger is a conductor.
However, if judgment is made as to whether a crew is present or as to discrimination between an adult and a child with the load sensor, a child seat strongly fasten to the seat with the seatbelt may cause an erroneous judgment such that an adult sits on the seat because of a great load on the load sensor.
Thus, it is required to provide a seat occupation judging apparatus for a vehicle capable of discrimination between an adult sitting on the seat and a child seat strongly fasten with a seat belt.
The aim of the present invention is to provide a superior seat occupation judging apparatus.
According to the present invention, a first aspect of the present invention provides a seat occupation judging apparatus for a vehicle comprising:
load detection means arranged at a seat for detecting a load on said seat to output a load detection signal;
seat condition detection means arranged at said seat for detecting a seat condition to generate a seat condition detection signal indicative of discrimination in presence on said seat between an adult and a child seat on said seat; and
judging means responsive to said load detection means and said seat condition detection means for outputting a judging signal indicating that a child seat is set on the seat when said load detection signal indicates that an adult sits on said seat and said seat condition detection signal indicates that said child seat set on said seat.
According to the present invention, a second aspect of the present invention provides a seat occupation judging apparatus based on the first aspect, wherein said seat condition detection means comprises a statistic field sensor including: a transmission electrode arranged in said seat in an outer layer, touchable to a seat occupation, of said seat; an alternative current source for supplying an alternative current to said transmission electrode; a capacitance detection circuit for detecting an electrostatistic capacitance provided by said transmission electrode with said alternative current and generating a seat condition detection result as said seat condition detection signal on the basis of said detected capacitance.
According to the present invention, a third aspect of the present invention provides a seat occupation judging apparatus based on the second aspect, wherein said transmission electrode is arranged at a first portion of said seat, said statistic field sensor further comprising a receiving electrode arranged in an outer layer touchable to said seat occupation at a second different portion of said seat for receiving a voltage induced by said transmission electrode and said alternative current; a capacitance variation detection circuit for detecting variation in capacitance provided by said transmission electrode and said receiving electrode with said alternative current and outputting another seat condition detection result indicating that an adult sits on said seat.
According to the present invention, a fourth aspect of the present invention provides a seat occupation judging apparatus based on the third aspect, wherein said judging means judges that said seat condition detection signal indicates that said seat occupation is an adult from a logical OR operation between said seat condition detection result and said another seat condition detection result.
According to the present invention, a fifth aspect of the present invention provides a seat occupation judging apparatus based on the second aspect, wherein said seat includes a sitting portion and a seat back, said sitting portion has a seat heater therein, said transmission electrode is arranged between a surface touchable to said seat occupation and said seat heater, of said sitting portion.
According to the present invention, a sixth aspect of the present invention provides a seat occupation judging apparatus based on the third aspect, wherein said seat includes a sitting portion and a seat back, said seat back has a seat heater therein, and said receiving electrode is arranged between a surface touchable to said seat occupation and said seat heater, of said seat back.
According to the present invention, a seventh aspect of the present invention provides a seat occupation judging apparatus based on the fifth aspect, further comprising an electrical conductive film with a high impedance condition between said seat heater of said sitting portion and said transmission electrode.
According to the present invention, an eighth aspect of the present invention provides a seat occupation judging apparatus based on the sixth aspect, further comprising a conductive film with a high impedance condition between said seat heater of said seat back and said receiving electrode.
According to the present invention, a ninth aspect of the present invention provides a seat occupation judging apparatus based on the first aspect, wherein said seat condition detection means comprises a planar pressure sensor array arranged in a sitting portion of said seat along a surface, touchable to said seat occupation, of said sitting portion including pressure sensing elements two-dimensionally arranged with a predetermined pattern.
According to the present invention, a tenth aspect of the present invention provides a seat occupation judging apparatus based on the ninth aspect, wherein said judging means analyzes a pressure pattern in a with direction of said seat and judges that said seat occupation is a person including an adult and a child when said analyzed pressure pattern has two peaks.
According to the present invention, an eleventh aspect of the present invention provides a seat occupation judging apparatus based on the ninth aspect, wherein a distance between centers of the leftmost and rightmost pressure elements in width direction is from 200 mm to 250 mm and a distance between centers, in the backward and forward direction of said sitting portion, of pressure elements at the front end of said sitting portion and the rear end of said sitting portion is from 70 mm to 130 mm.
According to the present invention, a twelfth aspect of the present invention provides a seat occupation judging apparatus based on the ninth aspect, wherein said array includes three to ten rows of said pressure elements arranged in said backward and forward direction of said sitting portion and five to twelve lines of pressure elements arranged in the width direction of said sitting portion at a predetermined interval.
According to the present invention, a thirteenth aspect of the present invention provides a seat occupation judging apparatus based on the twelfth aspect, wherein said array includes five line of said pressure elements arranged in said width direction, said pressure elements at a center one of said five line are arranged in a center line of said sitting portion in said width direction, and intermediate lines out of said five lines between the rightmost and leftmost ones of said five lines and said center one of said five lines are arranged closer to the rightmost and left most ones than said center one, respectively.